The present invention relates generally to catheters systems. In particular, the present invention is directed to a catheter system that provides for the controlled longitudinal movement of an elongate elementxe2x80x94such as a rotatable imaging core with an ultrasonic transducer or an optical fiber imaging device at its distal end, or a drive cable with an atherectomy cutter at its distal endxe2x80x94housed within a sheath positioned within a patient.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheromas or plaque, on the walls of blood vessels. Such deposits occur in both peripheral blood vessels which feed the limbs of the body and the coronary vessels which feed the heart. When the deposits accumulate in localized regions of a blood vessel, stenosis, or narrowing of the vascular channel, occurs. Blood flow is restricted and the person""s health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilate a region of atheroma, and other devices that are pushed or pulled along or through a deposit, such as atherectomy where a blade or cutting bit is used to sever and remove the atheroma, spark gap reduction in which an electrical spark burns through the plaque, laser angioplasty where laser energy is used to ablate at least a portion of the atheroma, and opening of vessels through the use of stents.
Two major difficulties in using such devices are maintaining a constant translational rate for the device and obtaining images of and information on the region of the blood vessel to be treated. Several imaging techniques have been proposed. Catheters incorporating mechanical rotation of ultrasonic transducers for imaging are disclosed in U.S. Pat. Nos. 4,794,931; 5,000,185; 5,049,130; and 5,024,234. These catheters scan in a plane normal to the catheter axis. Catheters employing phased array imaging systems are disclosed in U.S. Pat. Nos. 4,841,977 and 4,917,097. Catheters employing fiber optic imaging components are also known.
Generally deposits extend some longitudinal distance along the length of a vessel. To view different portions of the deposit a physician typically moves a handle attached to a proximal end of the imaging catheter along the vessel, for example, by pushing or pulling the catheter.
Imaging using computer-assisted reconstruction algorithms enables physicians to view a representation of the patient""s interior intravascular structures in two or three dimensions (i.e., so-called three-dimensional or longitudinal view reconstruction). In this connection, image reconstruction algorithms typically employ data-averaging techniques which assume that the intravascular structure between an adjacent pair of data samples will simply be an average of each such data sample. Thus, the algorithms use graphical xe2x80x9cfill inxe2x80x9d techniques to depict a selected section of a patient""s vascular system under investigation. Of course, if data samples are not sufficiently closely spaced, then lesions and/or other vessel abnormalities may in fact remain undetected (i.e., since they might lie between a pair of data samples and thereby be xe2x80x9cmaskedxe2x80x9d by the image reconstruction algorithms mentioned previously).
Even with the most skilled physician, it is practically impossible to manually exercise sufficiently slow constant rate longitudinal translation of the ultrasound imaging device (which thereby provides for a precisely known separation distance between adjacent data samples). In addition, with manual translation, the physician must manipulate the translation device while observing the conventional two-dimensional sectional images. This division of the physician""s attention and difficulty in providing a sufficiently slow constant translation rate can result in some diagnostic information being missed. To minimize the risk that diagnostic information is missed, it is necessary to lengthen the imaging scan time which may be stressful to the patient. Similarly, it is difficult for physicians to manually control the translational rate of atherectomy catheters and other interventional devices that are longitudinally advanced and retracted through blood vessel and other body lumens.
U.S. Pat. No. 5,485,846 discloses an ultrasound imaging transducer which is capable of being translated longitudinally within a section of a patient""s vascular system at a precise constant rate through the use of a longitudinal translation assembly. The longitudinal translation assembly moves the entire rotary drive assembly to provide the desired longitudinal movement of the transducer. Such an ability enables a series of precisely separated data samples to be obtained thereby minimizing (if not eliminating) distorted and/or inaccurate reconstructions of the ultrasonically scanned vessel section (i.e., since a greater number of more closely spaced data samples can reliably be obtained). Also, such an assembly can be operated in a xe2x80x9chands-offxe2x80x9d manner which allows the physician to devote his or her attention entirely to the real-time images with the assurance that all sections of the vessel are displayed. While such a longitudinal translation assembly can work well, it is relatively large, bulky and heavy; it is expensive; and it is cumbersome to set up, in part because the rotary drive and longitudinal translation assemblies are wrapped in separate sterile drapes (plastic bags) for sterility.
One drawback with conventional catheter imaging systems is the cost of replacing the disposable catheter assembly. The catheter assembly is mounted to a draped pullback assembly for use, used and then discarded after use. However, the catheter assembly includes the electronics necessary to send, receive and filter signals. These electronic components are disposed of with the rest of the catheter assembly which raises the cost of the procedure.
The present invention provides an automatic pullback catheter system in which costly electronic signal processing components can be removed from the disposable catheter assembly and incorporated into the drive assembly. This helps reduce the cost of each use. With the present invention, the catheter assembly need only include the sheath, the elongate operative element within the sheath, the drive connector, and the data/information connector, typically a coaxial electrical connector. The drive and data/information connectors are preferably combined into a combined connector. The resulting structure is compact, simple to use, and reduces the cost of the disposable catheter assembly.
The drive assembly includes a body to which a drive chassis is mounted for movement along a longitudinal path by a longitudinal driver. The longitudinal driver typically includes a motor which rotates a longitudinal drive screw selectively coupled to the drive chassis by a threaded clamp or clutch. The drive assembly also includes a rotary driver mounted to the drive chassis and movable with the drive chassis along the longitudinal path. The rotary driver includes a rotary drive motor and a first combined connector rotatable by the rotary drive motor.
The catheter assembly includes a hollow sheath housing an elongate operative element, typically a rotatable imaging core or cable having an imaging element at its distal end. The sheath includes a proximal portion removably mounted to the body. The catheter assembly also includes a rotatable and axially movable second combined connector connected to the proximal end of the cable or other operative element. The second combined connector is preferably housed within the proximal portion of the sheath.
The first and second combined connectors are preferably blind matable connectors to facilitate mounting the catheter assembly to and dismounting the catheter assembly from the drive assembly. The combined connectors provide for the transfer of information/data from the operative element to the drive assembly as well as for both the longitudinal movement coupling of the two combined connectors and the rotary movement coupling of the two combined connectors. Therefore, rotating the first combined connector by the rotary drive motor mounted to the drive chassis rotates the second combined connector thereby rotating the elongate operative element. Likewise, actuating the longitudinal driver drives the drive chassis along the longitudinal path which causes the longitudinal movement of the operative element within the sheath.
The drive chassis is preferably mounted to the body along a linear bearing. Using a linear bearing helps to ensure that the longitudinal movement of the drive chassis is smooth, encounters little friction and is very stable. Using a manually actuated threaded clamp to selectively secure the drive chassis to the longitudinal drive screw permits the user to decouple the drive chassis from the longitudinal drive shaft when desired and manually move the drive chassis, and thus the imaging element at the distal end of the imaging core, to the desired longitudinal position.
Another advantage of the invention results when the connection between the first and second combined connectors is a blind matable connection. That is, the connectors need only be properly aligned so pushing the two connectors together causes them to properly mate. Preferably, the data/information connection is made using coaxial plug and socket connectors which not only provide the desired electrical, optical or other type of connection, but also provides sufficient frictional engagement between the first and second combined connectors to permit the longitudinal movement of the elongate operative element (e.g. cable) within the sheath. While the frictional engagement between the two data/information connectors may be enough to provide an acceptable rotary drive interface, it is preferred that the first and second combined connectors include first and second rotary drive connectors including rotary drive surfaces. These rotary drive surfaces are preferably arranged to guide the two connectors into proper rotary alignment when engaged.
The proximal portion of the cable is preferably much stiffer than the remainder of the cable. This helps to ensure a fluid-tight seal can be provided between the cable and the proximal portion of the sheath. This is important when a fluid or flush port is provided distally of such seal; the seal helps to prevent the fluid from entering into the drive assembly. In addition, this stiff, proximal portion can be made sufficiently long so that when the rotary driver is in the longitudinally pulled-back or proximal position, only the stiff proximal portion of the cable is exterior of the sheath and inside the drive assembly. The stiff portion of the cable is stiff enough to be self-supporting and does not droop within the drive assembly. Pushing the cable distally is also facilitated by the use of a cable with a stiff proximal portion.
Other features and advantages will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.